A Neptunian orbit-sized parallax baseline would be very helpful in making that 3D dark-matter map that Christopher Jablonski thought of. We could at least find out how much of what we detect is inside our galaxy.

The blue cluster in M31 is very compact, fitting within 1/3 of a light-year. The two main peaks of the old red stars in the background nucleus are only 5 ly apart. The angular scale of the image is only 3 arcseconds across, so this a very extreme “zoom” into the center of M31.

Can they detect distance as well as direction? Perhaps with parallax? What would a 3D dark matter map look like? Does dark matter tend to clump together? Do I have a lot of questions about dark matter or what?